You get samsung exynos chip in the international version vs the snapdragon 845 in the US model. Thats the only difference. Alot of people insist snapdragon gives better standby time than exynos but i dont really see a difference on mine, it still lasts forever on a charge.
Note 9 is pretty much a very slightly larger s9+ with a bigger screen, battery , more storage and optionally more ram + the bluetooth s pen.
This is what i bought
If you are worried about warranty though you should stick with the US versions.